Células T de Memória Central para Imunoterapia

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Central memory self�tumor-reactive CD8� T cells
confer superior antitumor immunity compared
with effector memory T cells
Christopher A. Klebanoff*†‡, Luca Gattinoni†‡, Parizad Torabi-Parizi*§, Keith Kerstann†, Adela R. Cardones¶,
Steven E. Finkelstein†, Douglas C. Palmer†, Paul A. Antony†, Sam T. Hwang¶, Steven A. Rosenberg†,
Thomas A. Waldmann�, and Nicholas P. Restifo†**
*Howard Hughes Medical Institute, National Institutes of Health Research Scholars Program, Bethesda, MD 20814; and Branches of †Surgery,
¶Dermatology, and �Metabolism, National Cancer Institute, and §Laboratory of Immunology, National Institute of Allergy and Infectious Diseases,
National Institutes of Health, Bethesda, MD 20892
Contributed by Thomas A. Waldmann, May 6, 2005
Central memory CD8� T cells (TCM) and effector memory CD8� T
cells (TEM) are found in humans and mice; however, their relative
contributions to host immunity have only recently been examined
in vivo. Further, the ability of TCM to treat an established tumor or
infection has yet to be evaluated. To address the therapeutic
potential of different tumor-reactive CD8� T cell memory subsets,
we used an established model for the in vitro generation of TCM
and TEM by using IL-15 and IL-2, respectively. Adoptively trans-
ferred TCM exhibited a potent in vivo recall response when com-
bined with tumor-antigen vaccination and exogenous IL-2, leading
to the eradication of large established tumors. By contrast, TEM
were far less effective on a per-cell basis. Microarray analysis
revealed that the signature of highly in vivo effective antitumor T
cells included the overexpression of genes responsible for traffick-
ing to secondary lymphoid tissues. This gene expression profile
correctly predicted the in vitro and in vivo lymphoid-homing
attributes of tumor-reactive T cells. Furthermore, we found that
homing to secondary lymphoid tissue is required for optimal tumor
treatment. Our findings indicated that highly in vivo effective
antitumor T cells were those that initially targeted secondary
lymphoid tissue, rather than tumor sites, as had previously been
postulated. Thus, tumor-reactive CD8� T cell populations with the
phenotypic and functional attributes of TCM may be superior to
TEM�effector T cells for adoptive immunotherapies using concom-
itant tumor-antigen vaccination.
IL-2 � IL-15 � � homing � immunotherapy � vaccine
Adoptive cancer immunotherapy, the infusion of tumor-reactive T cells to patients, represents a promising approach
for the treatment of advanced metastatic disease (1, 2). To date,
cell types with effector T cell (TEFF) and effector memory CD8�
T cell (TEM) phenotype and function have been the cells targeted
for transfer because of their strong lytic capacity and release of
high levels of IFN-� (3, 4). Although transfer of polyclonal
tumor-reactive TEFF can cause an objective response rate ap-
proaching 50% (5), there are reasons to believe that transfer of
cells with memory properties, including a heightened recall
response and the ability to undergo self-renewal, may be superior
mediators of an antitumor response (6, 7).
The T cell memory compartment can be subdivided into two
populations, central memory CD8� T cells (TCM) and TEM, on
the basis of phenotypic markers, functional attributes, and
migratory properties (7). CD62L and CCR7, two surface mol-
ecules necessary for cellular extravasation in high endothelial
venules, are constitutively expressed by TCM, whereas these
markers are significantly down-regulated on TEM. TCM have been
shown to be superior to TEM in conferring protective immunity
against viral or bacterial challenge (8, 9). However, the extent to
which these results can be generalized has been questioned (10),
and the potential of TCM to treat an established infection or
cancer has not been evaluated.
To assess the in vivo role of different CD8� T cell memory
subsets, we used an established in vitro culture system by using
IL-15 and IL-2 to generate TCM and TEM, respectively (8, 11–13).
To generate tumor-reactive CD8� T cells, we used cells from
pmel-1 T cell receptor transgenic mice. Pmel-1 mice have CD8�
T cells that have specificity for a Db-restricted epitope corre-
sponding to amino acid positions 25–33 of the nonmutated
self�tumor antigen (Ag) gp100 (14). The two cell subtypes were
verified by using global analysis of gene expression as well as
phenotypic and functional characteristics. We found that adop-
tive cell transfer (ACT) of self�tumor-reactive CD8� TCM was a
superior mediator of tumor treatment compared with TEM.
Materials and Methods
Mice and Tumor Lines. Pmel-1 T cell receptor transgenic mice
expressing CD8� T cells with specificity for a Db-restricted
epitope from the nonmutated self�tumor Ag gp10025–33 (14)
were crossed with C57BL�6-thy1.1 transgenic and C57BL�6-
Sell�/� mice (both from The Jackson Laboratory) to derive
pmel-thy1.1 (deposited at The Jackson Laboratory, www.jax.org)
and pmel-CD62L�/� (pmel CD62L knockout) mice (26), respec-
tively. Female C57BL�6 and B6.129S2-Ltatm1Dch�J (both from
The Jackson Laboratory) and �2-microglobulin (�2M)-deficient
(�2M�/�) mice (Taconic Farms) were used as recipients in ACT
experiments. B16 (H-2b), a spontaneous gp100� murine mela-
noma, has been described (14). Experiments were conducted
with the approval of the National Cancer Institute Animal Use
and Care Committee.
TCM and TEM Generation and Adoptive Immunotherapy. Pmel-1
splenocytes were isolated and cultured in the presence of 1 �M
human gp10025–33 (hgp10025–33) and complete medium contain-
ing 10 ng�ml of either recombinant human IL-2 (Chiron) to
generate pmel TEM or recombinant human IL-15 (PeproTech,
Rocky Hill, NJ) to generate pmel TCM (12). Mice (n � 5) were
injected s.c. with 2–5 � 105 B16-F10 melanoma cells. Nine days
later, mice were treated with i.v. ACT of pmel TCM or TEM.
Where specified, transient lymphopenia was induced by suble-
thal irradiation (500 cGy) of tumor-bearing mice on the day of
treatment. Vaccination was achieved with 2 � 107 plaque-
forming units of a recombinant fowlpox virus encoding hgp100
Abbreviations: Ag, antigen; hgp100, human gp100; rFPhgp100, recombinant fowlpox virus
encoding hgp100; TEM, effector memory CD8� T cells; TCM, central memory CD8� T cells; LN,
lymph node; ACT, adoptive cell transfer; DC, dendritic cell; CFSE, carboxyfluorescein
diacetate succinimidyl ester; LT�, lymphotoxin-�; �2M, �2-microglobulin; BM, bone
marrow.
‡C.A.K. and L.G. contributed equally to this work.
**To whom correspondence should be addressed. E-mail: restifo@nih.gov.
www.pnas.org�cgi�doi�10.1073�pnas.0503726102 PNAS � July 5, 2005 � vol. 102 � no. 27 � 9571–9576
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(rFPhgp100) as described (Therion Biologics, Cambridge, MA)
(14). Recombinant human IL-2 was administered by i.p. injec-
tion twice daily at 36 �g per dose for a total of six doses. Murine
bone marrow (BM)-derived dendritic cells (DCs) were gener-
ated as described (15). The products of the perpendicular
diameters (mean � SEM) of tumors for tumor growth curves
were measured in a blinded fashion with calipers. All experi-
ments were repeated at least twice with similar results.
Microarray and Flow Cytometric Analysis of TCM and TEM. Pmel TCM
and TEM were isolated to a purity of �95% by using a no-touch,
negative selection CD8-enrichment column (Miltenyl Biotech,
Auburn, CA). RNeasy column (Qiagen, Germantown, MD)-
purified RNA was indirectly labeled with a single round of linear
amplification with Amino Allyl MessageAmp reagents (Ambion,
Austin, TX). Labeled samples were combined and hybridized
overnight to 22,000-gene long-oligo arrays supplied by the
National Cancer Institute (Frederick, MD). Data image files
were obtained with a GenePix 4000B scanner (Axon Instru-
ments, Union City, CA) and imported into GENESPRING 6.2
software (Silicon Genetics, Redwood City, CA).
Ex Vivo Analysis of Adoptively Transferred Cells. All antibodieswere
purchased from BD Pharmingen except anti-human granzyme
B-phycoerythrin (GB11) (Caltag, Burlingame, CA). FACS-
calibur f low cytometer and CELLQUEST software (BD Bio-
Sciences, Franklin Lakes, NJ) were used to analyze cells.
Adoptively transferred cells in inguinal, axillary, and mesen-
teric lymph nodes (LNs) were analyzed by cytof luorometry for
carboxyf luorescein diacetate succinimidyl ester (CFSE),
thy1.1, and CD8. For immunohistochemical staining, inguinal
LNs were snap-frozen, stored at �80°C, then sectioned at
7-�m cuts by using cryostat. Sections were Fc-blocked before
staining with 10 �g�ml purified anti-PNAd (BD Pharmingen)
followed by Cy5-conjugated secondary antibody (Caltag).
Sections were mounted with a ProLong Antifade Kit (Molec-
ular Probes) and allowed to stand at room temperature
overnight. Images were obtained on a Nikon Eclipse confocal
laser-scanning microscope (Bio-Rad). In vitro proliferation of
pmel TEM and TCM was evaluated by labeling cells with 1 �M
CFSE (Molecular Probes) and restimulating with 1 �M
hgp10025–33-pulsed irradiated splenocytes in complete medium
containing 2 ng�ml of recombinant human IL-2.
In Vitro Rolling Assay. Rolling of pmel TEM, pmel TCM, and
CD8-enriched naı̈ve cells was determined on 35-mm cell sus-
pension plates (430588) (Corning) coated with GlyCAM-1 (a
gift from S. D. Rosen, University of California, San Francisco),
E-selectin (R & D Systems), or 1% BSA in PBS, held overnight
at 4°C, and blocked with 1% BSA for 1 h at 4°C. Calcein-
acetomethyl-labeled (Molecular Probes) T cells were injected at
1.5 dynes per cm2 into a parallel plate flow chamber (Glycotech,
Gaithersburg, MD). Cells were digitally photographed (�1
image per s) in four to six random fields (each field � 1.18 mm2)
with excitation at 488 nm and emission at 513 nm, and nonmov-
ing and moving cells were differentiated with the IPLAB software
program (Scanalytics, Fairfax, VA) and compared by using the
Student t test.
Fig. 1. Trafficking of tumor-reactive CD8� T cells to 2° lymphoid tissues is required for antitumor treatment. (A) WT or LT��/� mice bearing 9-day s.c. B16 tumors
were left untreated as controls (F and E, respectively) or received 1 � 106 pmel TEM, rFPhgp100 vaccination, and exogenous IL-2 (■ and �, respectively). (B) CD62L
expression by adoptively transferred tumor-reactive CD8� T cells is required for optimal antitumor treatment. WT mice bearing 9-day s.c. B16 melanoma tumors
were treated with nothing (F), pmel-CD62L�/� cells (�), or age-matched pmel-CD62L�/� cells (■ ) in combination with rFPhgp100 and exogenous IL-2. (C)
Redundancy of lymphoid-homing molecules. Splenocytes from pmel-CD62L�/� or age-matched pmel-CD62L�/� controls were stimulated with 1 �M hgp10025–33
peptide and cultured under TEM conditions. Cells were cytofluorometrically analyzed on day 6 for the expression of integrin �E, integrin �7, and CCR7. Numbers
represent the percentage of gated cells in each quadrant after gating on propidium iodide-negative and CD8� lymphocytes. (D) Tumor treatment fails in �2M�/�
hosts, but can be rescued by cotransfer of BM-derived DCs. WT or �2M�/� mice bearing 9-day B16 tumors were left untreated as controls (F and E, respectively)
or received 1 � 106 TEM pmel, rFPhgp100, and exogenous IL-2 (■ and �, respectively) � cotransfer of mature BM-derived DCs (Œ).
9572 � www.pnas.org�cgi�doi�10.1073�pnas.0503726102 Klebanoff et al.
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Results
Trafficking to 2° Lymphoid Tissues Is Required for Optimal Antitumor
Treatment. Altered peptide ligand (14, 15) vaccine-encoded
tumor Ag presentation by professional Ag-presenting cells pro-
motes optimal antitumor immunity (16). We therefore hypoth-
esized that trafficking of adoptively transferred cells to 2°
lymphoid organs could lead to an enhanced in vivo antitumor
response. To evaluate the lymphoid trafficking requirements of
adoptively transferred pmel cells, we compared the tripartite
treatment regimen of cells, rFPhgp100 vaccination, and exoge-
nous IL-2 in tumor-bearing C57BL�6 (WT) and lymphotoxin-
��/� (LT��/�) mice. LT��/� mice lack peripheral lymphoid
structures, including LNs and mucosal Peyer’s patches, and
possess a disorganized splenic white pulp (17). To provide a
treatment window, we intentionally transferred a noncurative
dose (1 � 106) of pmel TEM. There was no statistical difference
in tumor growth between untreated WT and LT��/� mice (P �
0.8550) (Fig. 1A). As previously shown by our group, the
combination of pmel TEM, vaccination, and IL-2 caused a
pronounced delay in tumor growth in WT mice compared with
untreated controls (P � 0.0001) (12, 14, 18). By contrast, the
antitumor effect was completely abrogated in LT��/� mice.
There was no statistical difference in tumor growth between
untreated LT��/� mice and LT��/� mice that received cells,
vaccine, and IL-2 (P � 0.6200). Thus, 2° LNs were required in
the tumor-bearing host for optimal tumor treatment.
To determine the influence of L-selectin (CD62L), a critical
mediator of lymphocyte homing to 2° LNs (19), we adoptively
transferred TEM from pmel-CD62L�/� or age-matched pmel-
CD62L�/� controls in combination with vaccine and IL-2 into
tumor-bearing WT mice. Although treatment with either TEM
pmel-CD62L�/� or pmel-CD62L�/� cells resulted in delayed
tumor growth compared with untreated controls (P � 0.0018 and
� 0.001, respectively), pmel-CD62L�/� cells conferred superior
treatment efficacy compared with pmel-CD62L�/� cells (P �
0.0091) (Fig. 1B). Thus, CD62L was functionally important for
antitumor T cell function in vivo. Phenotypic analysis revealed,
however, that the overexpression of other LN-homing receptors
might partially compensate for the lack of CD62L, including
integrin �7, integrin �E, and CCR7 (Fig. 1C).
Fig. 2. Gene expression profiling and FACS analysis of self�tumor-reactive
CD8� TCM vs. TEM. (A) A selected summary of microarray results. Shown in green
are the genes involved in trafficking to 2° lymphoid organs; the hatched green
bar indicates a gene (mcl1) that has antiapoptotic activity; shown in red are
genes involved in effector functions; and hatched red bars indicate proapo-
ptotic genes. (B) Cytofluorometric validation of microarray results of pmel TCM
and TEM. Surface expression of CD62L and integrin �E are shown with the
percentages of CD8� lymphocytes in each quadrant or the mean fluorescence
intensity (MFI) for intracellular granzyme B.
Fig. 3. LN-homing attributes of tumor Ag-specific CD8� TCM vs. TEM. (A and
B) Pmel TCM but not TEM roll efficiently on substrates coated with glycam-1, a
ligand for CD62L. Calcein-acetomethyl-labeled pmel TCM, TEM, or CD8-
enriched naı̈ve cells were injected at 1.5 dynes per cm2 into a parallel plate
flow chamber in which the bottom plate was coated with glycam-1, E-selectin,
or BSA. After 4 min, rolling cells were photographed (four to six random fields
per condition) and counted in a blinded fashion (mean � SD). (C and D) In vivo
LN homing of pmel TCM vs. TEM. CFSE-labeled, pmel-thy1.1 TCM and TEM were
adoptively transferred into separate Thy1.2 WT mice, and LNs were extracted
24 h later. (C) Cryostat sections of inguinal LNs 24 h after ACT of 4 � 106
CFSE-labeled (green) pmel TCM (Lower) or TEM (Upper). High endothelial
venules were identified by staining for PNAd followed by Cy5-conjugated
secondary antibody (blue). (D) Cytofluorometric analysis for CFSE�CD8� cells
from homogenized peripheral LNs and Peyer’s patches of recipient mice 24 h
after ACT.
Klebanoff et al. PNAS � July 5, 2005 � vol. 102 � no. 27 � 9573
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To test whether homing of adoptively transferred pmel-1 cells
to LNs facilitated their interaction with resident professional
Ag-presenting cells expressing the vaccine-encoded hgp10025–33,
we compared the treatment efficacy of our tripartite regimen in
tumor-bearing WT versus �2M�/� mice. Tumor growth was
identicalin untreated WT and �2M�/� controls (P � 0.963) (Fig.
1D). The tripartite regimen of cells, vaccine, and IL-2 was
effective at delaying tumor growth in WT mice (P � 0.0034) but
was not effective in the same experiment in mice incapable of
presenting MHC class I-restricted Ags (untreated vs. treated
�2M�/� mice P � 0.05). This lack of treatment effect could be
partially rescued by the cotransfer of �2M-intact mature BM-
derived DCs (P � 0.009 vs. no treatment). No rescue was
observed when DCs were generated from �2M�/� mice (data not
shown). Thus, we determined that trafficking of adoptively
transferred tumor-reactive CD8� T cells to organized 2° lym-
phoid tissues was necessary for optimal in vivo antitumor efficacy
in a combined immunotherapy treatment regimen that includes
tumor-Ag vaccination.
Gene Expression Profiling of CD8� TCM vs. TEM. Because trafficking
to 2° lymphoid tissues by adoptively transferred pmel cells
facilitated their in vivo antitumor efficacy, we sought to create T
cells with enhanced LN-homing attributes. Naı̈ve, peptide-
stimulated CD8� T cells expanded in the presence of IL-15 give
rise to in vitro differentiated TCM, whereas IL-2 caused the
expansion of TEM that lost the expression of the LN-homing
markers CD62L and CCR7 (8, 12, 13). To more fully charac-
terize the attributes of these two cell populations, we performed
microarray analysis (GEO accession nos. GSE2578 and
GSM49518, www.ncbi.nlm.nih.gov�geo). A total of 476 of the
22,000 genes sampled were differentially expressed between
pmel TCM and TEM. Remarkably, genes associated with homing
to 2° lymphoid tissues, including integrin aE, cd62l, ly6c, cxcr3,
and ccr7, were among those RNAs overexpressed by pmel TCM
compared with TEM (Fig. 2A). Additionally, mcl1, an antiapo-
ptosis molecule implicated in the maintenance of mature T
lymphocytes, was also up-regulated by TCM (20). By contrast,
genes associated with effector functions (granzyme A, B, C, D, F,
G, H, and perforin) and proapoptotic signaling (Bid, Bnip3, and
Bad) were among the most highly overexpressed in TEM (Fig.
2A). Microarray results for CD62L, integrin �E, and intracel-
lular granzyme B on pmel TCM and TEM were validated by
cytofluorometry (Fig. 2B). Consistent with previously published
FACS results, CD62L expression was notably higher in pmel TCM
than in TEM (12). Integrins �E (Fig. 2B) and �7 (data not shown)
were two additional lymphoid-homing molecules that were
overexpressed on pmel TCM. Conversely, pmel TEM exhibited a
higher level of granzyme B expression compared with pmel TCM
(mean fluorescence intensity � 998 and 499, respectively). These
data indicated that some of the most pronounced gene and
protein expression differences between pmel TCM and TEM
relate to the capacity to home to LNs and the acquisition of
effector functions, respectively.
In Vitro and in Vivo LN-Homing Attributes of Tumor Ag-Specific TCM
and TEM. To determine whether the gene and protein expression
profiling results of pmel TCM and TEM were reflected in func-
tional difference in tissue homing behavior, we evaluated the in
vitro rolling of pmel TCM and TEM under physiologic shear flow
conditions. We used substrates coated with glycam-1, a ligand for
CD62L expressed in the high endothelial venules of peripheral
LNs (19). Neither population of cells rolled on substrates coated
with BSA, an irrelevant protein control (Fig. 3A). Both pmel TCM
and CD8-enriched naı̈ve pmel-1 cells, a lymphocyte population
with optimal LN-homing attributes, rolled on glycam-1, whereas
pmel TEM did not (P � 0.01) (Fig. 3 A and B). TEM reportedly
display a characteristic pattern of surface chemokine and adhe-
Fig. 4. Enhanced in vivo recall response of tumor-Ag-specific CD8� TCM over TEM. (A–C) Sublethally irradiated WT mice bearing 9-day established B16 tumors
were left untreated as controls (F) or received the tripartite combination of rFPhgp100, exogenous IL-2, and 1 � 106 pmel TCM (■ ) or TEM (�). Absolute numbers
of adoptively transferred pmel-1 cells (identified by CD8�V�13� lymphocytes) were enumerated in the spleens or blood of treated animals as a function of time.
Each data point represents the average of at least two mice per group. For comparison, the mean absolute lymphocyte count (� SEM) of five nonirradiated
tumor-bearing WT mice is shown (Œ). (D) Comparison of the intrinsic proliferative capacity of restimulated pmel TCM vs. TEM. Pmel-thy1.1 cells expanded under
TCM (light lines) or TEM (bold lines) conditions were CFSE-labeled, then restimulated with irradiated WT splenocytes pulsed with hgp10025–33 peptide in complete
media containing IL-2. CFSE dilution was determined by daily FACS analysis after gating on CD8�thy1.1� lymphocytes.
9574 � www.pnas.org�cgi�doi�10.1073�pnas.0503726102 Klebanoff et al.
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sion molecules required for homing to inflamed peripheral
tissues (7). To test this capacity, we assayed rolling of in
vitro-generated pmel TCM and TEM on substrates coated with
E-selectin, a leukocyte adhesion molecule expressed on endo-
thelial cells at inflammatory sites. Both cell types rolled on this
substrate (Fig. 3A); however, a greater number of pmel TEM
compared with TCM was found on E-selectin (P � 0.05). There-
fore, pmel TEM possessed in vitro properties consistent with an
enhanced propensity to traffic to inflamed peripheral tissues,
whereas pmel TCM displayed enhanced LN-homing attributes.
We next investigated the in vivo LN-homing properties of
these two cell populations. We adoptively transferred CFSE-
labeled pmel-thy1.1 TCM and TEM into thy1.2 C57BL�6 hosts.
Twenty-four hours after ACT, we extracted peripheral LNs of
recipient mice for immunohistochemical staining and FACS
analysis. Grossly, immunohistochemical staining of inguinal LNs
24 h after ACT revealed a pronounced accumulation of adop-
tively transferred CFSE-labeled cells in animals that received
pmel TCM, but not TEM (Fig. 3C). Cytofluorometric analyses of
peripheral LNs was performed to quantitate these results, and
multiple independent experiments confirmed that there was
between 20 and 40 times the number of CFSE�CD8� cells
present in lymphoid tissues in animals that received pmel TCM
compared with TEM (Fig. 3D). These results were not caused by
differential CFSE dilution by pmel TEM because similar results
were obtained by analysis for CD8� Thy1.1� cells (data not
shown). These data demonstrated that gene expression profiling
of pmel-1 cells expanded under TCM and TEM conditions accu-
rately depicted the in vitro and in vivo LN-homing attributes of
these two populations of tumor-reactive CD8� T cells.
Enhanced in Vivo Recall Response and Tumor Treatment of TCM
Compared with TEM. To determine the functionality of TCM and
TEM in vivo, we adoptively transferred in vitro-differentiated
pmel subsets into sublethally irradiated tumor-bearing WT mice
in combination with vaccine and IL-2. The in vivo recall response
of these two cell populations (as assessed by the enumeration of
the absolute numbers of adoptively transferred pmel-1 cells in
the spleens and blood of treated animals) revealed that there was
a marked expansion of adoptively transferred TCM and TEM,
peaking in both groups �5 days after transfer (Fig. 4A). Impor-
tantly, the magnitude of the response in the spleens of mice that
received TCM was strikingly greater, peaking at levels four to 14
times higher than TEM in individual experiments. These results
were not caused simply by the differential accumulation of TCM
in the spleen because an analogous proliferation pattern was also
observed in the blood, a nonlymphoid tissue (Fig. 4 B and C).
Indeed, animals that received TCM experienced a true tumor-
reactive CD8� T cell lymphocytosis that was more than three
times the absolute lymphocyte count of WT mice, a phenome-
non not observed with TEM. The in vivo results were not caused
merely by intrinsic differences in proliferative capacity of TCM
over TEM, because there wasa similar rate of CFSE dilution in
these two cell populations in an ex vivo assay (Fig. 4D).
Pronounced lymphocytosis in melanoma patients treated with
ACT after lymphodepletion has been correlated with antitumor
efficacy (5). To determine whether the lymphocytosis observed
in mice treated with TCM correlated with the antitumor effect,
we treated sublethally irradiated mice bearing 9-day established
B16 melanoma with ACT at a dose of pmel cells (1 � 106)
previously established to be noncurative when TEM are used in
combination with vaccine and IL-2. As previously shown, the
suboptimal tripartite regimen using pmel TEM caused a pro-
nounced delay without cures in tumor growth compared with
untreated controls (P � 0.0069) (Fig. 5A). Treatment with TCM
delayed tumor growth significantly compared with both un-
treated controls (P � 0.0001) and TEM-treated mice (P �
0.0014). In addition, a TCM-based regimen caused improved
survival (P � 0.002) (Fig. 5B). Thus, ACT of a TCM population,
in combination with tumor-Ag vaccination and exogenous IL-2,
produced a more robust and therapeutically significant in vivo
recall response compared with TEM.
Discussion
Recent human trials for the adoptive immunotherapy of cancer
have demonstrated a statistical correlation between the persis-
tence of transferred tumor-reactive T cells and the therapeutic
response that could objectively be achieved in �50% of the
patients treated by using cells with TEM or effector T cell
phenotype (21). Although preliminary work using viral Ags has
suggested that TCM are superior mediators of a recall response
to Ag challenge (8, 9), some have recently called these findings
into question (10). In the present studies, we evaluated the role
of TEM and TCM populations as mediators of an immune
response to an established disease. We found that Ag-specific
TCM mounted a heightened in vivo recall response compared
with TEM, consistent with other reports (9, 22). Importantly, this
enhanced response by TCM was associated with the complete
eradication of a large, established B16 melanoma. As seen in
other models, TEM can generate a 2° response but the relative
efficiency of this response was less than that of TCM on a per-cell
basis (9, 22).
Although TCM and TEM have been subdivided on the basis of
their relative expression of lymphoid-homing molecules (7, 11),
these two populations also possess other unique attributes. For
example, TEM have been shown to develop effector functions
more rapidly than TCM (7, 8). By contrast, TCM are able to release
significant amounts of helper cytokines, such as IL-2 (7, 9, 12).
Fig. 5. Tumor-reactive CD8� TCM are superior to TEM in the treatment of B16
melanoma. (A) Sublethally irradiated (5 Gy) WT mice bearing 9-day B16
tumors were left untreated as controls (F) or received rFPhgp100 vaccination,
exogenous IL-2, and either pmel TCM (■ ) or TEM (�). (B) Enhanced tumor
regression in mice receiving pmel TCM correlated with statistically prolonged
animal survival, compared with mice receiving TEM.
Klebanoff et al. PNAS � July 5, 2005 � vol. 102 � no. 27 � 9575
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In our own analysis of the differences between TCM and TEM by
using oligo microarrays, we found that expression of genes
associated with lymphoid homing were among the most highly
overexpressed by TCM. The critical importance of homing to 2°
LNs by adoptively transferred tumor-reactive T cells was estab-
lished by experiments in which tumor therapy was completely
abrogated in host mice with absent peripheral lymphoid tissues
and a disrupted splenic structure. Further evidence that traf-
ficking to LNs is required was provided by using tumor-reactive
CD8� T cells genetically deficient in CD62L.
T cell homing to 2° LNs was required to facilitate interaction
with virally infected BM-derived Ag-presenting cells, as evi-
denced by the absence of tumor treatment in �2M�/� hosts and
their rescue by cotransfer of WT BM-derived DCs. It is likely
that the enhanced in vivo proliferative response of TCM was the
result of increased access to vaccine-encoded Ag-expression in
2° LNs as both TCM and TEM exhibited similar intrinsic prolif-
erative responses when Ag levels were normalized in vitro. These
results indicated that, in addition to prevention, TCM can be a
superior mediator of a therapeutic response, and this effect
highly depended on the cells’ homing to lymphoid tissues.
The approach of targeting T cell trafficking to LNs provides
an alternative to attempts to cause the initial trafficking of
adoptively transferred immune cells to tumors directly (23).
These efforts have included the insertion of genes encoding
chemokine receptors into lymphocytes to enhance their recruit-
ment to tumor sites (24) and the genetic modification of the
tumor microenvironment itself through the forced expression of
LIGHT, a tumor necrosis factor superfamily member used to
enhance the recruitment, retention, and activation of T cells
(25). Thus, the alternative and perhaps complementary ap-
proach described here is the use of concomitant tumor-Ag
vaccination that induces a massive clonal expansion and subse-
quent infiltration of numerous tissues by antitumor T cells (18)
that obviates the requirement for immediate and specific tar-
geting of the tumor site.
These results have implications for the design of human
adoptive immunotherapy trials. In most currently used protocols,
the cells generated for ACT acquire effector T cell�TEM phe-
notypic and functional attributes before transfer (4). Our data
suggest that ACT of these populations may be suboptimal;
although response rates approaching 50% can now be obtained
with the transfer of very large numbers (up to 1 � 1011) of ex
vivo-expanded T cells (5). The transfer of a more efficient
antitumor TCM population might increase the proliferation and
persistence of cells upon adoptive transfer in vivo. Our findings
may have significant implications for the selection and the
generation of optimal antitumor T cells for ACT in cancer
patients. The generation of TCM may be accomplished by altering
duration and nature of T cell culture conditions in human clinical
trials.
C.A.K. dedicates this manuscript to Grandma Anne Anderson and her
personal battle with cancer. We thank D. Surman, P. J. Spiess, Z. Yu, and
Y. Lou for technical assistance.
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